Motorized apparatus for opening and closing sectional overhead doors has long been known in the art. These powered door operators developed in part due to extremely large, heavy commercial doors for industrial buildings, warehouses, and the like where opening and closing of the doors essentially mandates power assistance. Later, homeowners'demands for the convenience and safety of door operators resulted in an extremely large market for powered door operators for residential usage.
The vast majority of motorized operators for residential garage doors employ a trolley-type system that applies force to a section of the door for powering it between the open and closed positions. Another type of motorized operator is known as a "jack-shaft" operator, which is used virtually exclusively in commercial applications and is so named by virtue of similarities with transmission devices where the power or drive shaft is parallel to the driven shaft, with the transfer of power occurring mechanically as by gears, belts, or chains between the drive shaft and a driven shaft controlling door position. While some efforts have been made to configure hydraulically or pneumatically-driven operators, such efforts have not achieved any substantial extent of commercial acceptance.
The well-known trolley-type door operators are normally connected directly to the top section of a garage door and for universal application may be powered to operate doors of vastly different size and weight, even with little or no assistance from a counterbalance system for the door. Since the operating force capability of trolley-type operators is normally very high, force adjustments are normally necessary and provided to allow for varying conditions and to allow the operator to be tuned, depending on the application. When a garage door and trolley-type operator are initially installed and both adjusted for optimum performance, the overhead door system can perform well as designed. However, as the system ages, additional friction develops in door and operator components due to loss of lubrication at rollers and hinges. Also, the door can absorb moisture and become heavier, and counterbalance springs can lose some of their original torsional force. These and similar factors can significantly alter the operating characteristics seen by the operator, which may produce erratic door operation such as stops and reversals of the door at unprogrammed locations in the operating cycle.
Rather than ascertaining and correcting the conditions affecting door performance, which is likely beyond a howeowner's capability, or engaging a qualified service person, homeowners frequently increase the force adjustment to the maximum setting. Facilitating this cause for maximum settings is the fact that the force adjustment mechanism is normally conveniently accessible outside the motor housing of trolley-type operators, and adjustment to higher force settings appears to overcome many problems. A further cause for maximum force settings originates with installers who may be paid a fixed amount per installation, such that time considerations result in a maximum force setting rather than ascertaining the reason for and correcting the condition necessitating an inordinately high force setting. Also, return service calls, at least in the short term after installation, are sometimes at the installer's expense. This may motivate an installer to adjust the operator to the maximum force setting so that such a return service call becomes less likely. However, setting an operator on a maximum force adjustment creates an unsafe condition in that the operator becomes highly insensitive to obstructions. In the event a maximum force setting is effected on a trolley-type operator, the unsafe condition may also be dramatically exemplified in the event of a broken spring or springs. In such case, if the operator is disconnected from the door in the fully open position during an emergency or if faulty door operation is being investigated, one half or all of the uncounterbalanced weight of the door may propel the door to the closed position with a guillotine-like effect.
Another problem with trolley-type door operators is that they do not have a mechanism for automatically disengaging the drive system from the door if the door encounters an obstruction. This necessitates the considerable effort and cost which has been put into developing a variety of ways, such as sensors and encoders, to signal the operator controls when an obstruction is encountered. In virtually all instances, manual disconnect mechanisms between the door and operator are required to make it possible to operate the door manually in the case of power failures or fire and emergency situations where entrapment occurs and the door needs to be disconnected from the operator to free an obstruction. These mechanical disconnects, when coupled with a maximum force setting adjustment of the operator, can readily exert a force on a person or object which may be sufficiently high to bind the disconnect mechanism and render it difficult, if not impossible, to actuate.
In addition to the serious operational deficiencies noted above, manual disconnects, which are normally a rope with a handle, must extend within six feet of the floor to permit grasping and actuation by a person. In the case of a garage opening for a single car, the centrally-located manual disconnect rope and handle, in being positioned medially, can catch on a vehicle during door movement or be difficult to reach due to its positioning over a vehicle located in the garage. Trolley-type door operators raise a host of peripheral problems due to the necessity for mounting the operator to the ceiling or other structure substantially medially of and to the rear of the sectional door in the fully open position.
Operationally, precise alignment is also essential because the connecting arm of the operator is attached directly to the door and thus transmits forces to the door, totally independent of the counterbalance system. In the event of misalignment, the door can readily bind, thereby necessitating frequent adjustment or an undesirable increase in the force adjustment on the operator. It will thus be appreciated that the wider the door, the more significant a misalignment becomes. Further, if an overhead beam or other obstruction is located centrally of the door where an operator would normally be mounted, the off-center mounting of an operator requires added care in terms of compensation in the counterbalance system adjustment, not to mention the increased probability of developing misalignment which must be frequently corrected.
The position of the trolley above the door frequently results in essential lubricant and collected dirt being discharged to fall on the outside face of the door or the floor of a garage. Due to the required positioning of the motor unit of a trolley-type operator as described above, the necessity for mounting the motor housing in a position centrally of the garage and behind the door presents additional ancillary problems. Typically, the motor housing is mounted on perforated angle irons which are in turn mounted by a plurality of screws to the garage ceiling, which normally consists of sheetrock, plastering, or the like. The radial force vectors on the screws occasioned by reaction on the drive motor to door movement, particularly those attendant initial movement of the door, produce a fatigue failure of the ceiling material, which eventually results in a loosening of the attachment screws. This can result in the motor and trolley track weight overcoming the residual attachment screws holding force, thus causing the entire system to fall and possibly injure persons or damage objects below. Adequate inspection and servicing of the attachment screws to avoid holding failure requires inspection and work in close proximity to the drive gears, sprockets, chains, and the like, which frequently have few or no enclosure guards, thereby presenting the possibility of serious physical injury.
Another factor associated with the manner in which trolley-type operators are mounted relates to the attachment of the end of the trolley rail in the area proximate the door header. Commonly, the mounting bracket for a torsion-spring counterbalance system is attached to a spring mounting pad, which normally takes the form of a length of 2.times.6 wood that is mounted at substantially the center of the door above the header. Whether an original installation or a retrofit, the bracket that attaches the end of the trolley rail to the header is normally attached to the same mounting pad. These mounting pads, which are stressed to receive the resultant torque of the torsion springs, sometimes fail as by splitting when screws are driven into the mounting pad to mount the attachment bracket at the end of the trolley rail. Since the area above the header can be accessed only with the door closed, the counterbalance torsion springs are at their maximum tension. This splitting of the spring mounting pad releases the torsion-spring bracket and results in a powerful unloading of the torsion spring, which causes the mounting bracket to rotate rapidly, thus posing the possibility of serious injury to an installer in proximity to the operator.
A further area of concern with trolley-type operators is that the high-force capability of these operators is applied to the top panel of the door. Frequently, manufacturers add additional strengthening to the top panel, despite additional cost and weight, to prevent damage if an obstruction is encountered or if the door becomes misaligned and is retarded or jams. Thus, the basic operating principle and the necessary location and interface with the door both contribute to operational, safety, and cost disadvantages.
The commercial usage of jack-shaft operators has been limited virtually exclusively to commercial applications where a large portion of the door stays in the vertical position. This occurs where a door opening may be 15, 20, or more feet in height, with only a portion of the opening being required for the ingress and egress of vehicles. These jack-shaft operators are not attached to the door but attach to a component of the counterbalance system, such as the shaft or a cable drum. Due to this type of connection to the counterbalance system, these operators require that a substantial door weight be maintained on the suspension system, as is the case where a main portion of the door is always in a vertical position. This is necessary because jack-shaft operators characteristically only drive or lift the door from the closed to the open position and rely on the weight of the door to move the door from the open to the closed position, with the suspension cables attached to the counterbalance system solely controlling the closing rate.
Such a one-way drive in a jack-shaft operator produces potential problems if the door binds or encounters an obstruction upon downward movement. In such case, the operator may continue to unload the suspension cables, such that if the door is subsequently freed or the obstruction is removed, the door is able to free-fall, with the potential of damage to the door or anything in its path. Such unloading of the suspension cables can also result in the cables coming off the cable storage drums, thus requiring substantial servicing before normal operation can be resumed.
Jack-shaft operators are normally mounted outside the tracks and may be firmly attached to a door jamb rather than suspended from the ceiling or wall above the header. While there is normally ample jamb space to the sides of a door or above the header in a commercial installation, these areas frequently have only limited space in residential garage applications. Further, the fact that the normal jack-shaft operators require much of the door to be maintained in a vertical position absolutely mitigates against their use in residential applications where the door must be capable of assuming essentially a horizontal position since, in many instances, substantially the entire height of the door opening is required for entry and departure of vehicles.